Hi Brittany!
Yes, children of ALL ages (that's you and me, right?) can dress up as Disney Characters for Mickey's Not So Scary Halloween Party at the Magic Kingdom, after the hours of 4 p.m., which is when Guests are allowed entry for the event.
Just make sure that the costume is appropriate for all ages, and Disney prefers that you do not wear full facial masks (safety concerns, since you will be enjoying Disney rides and attractions during the event).
Also, you must not attempt to portray yourself as an actual Disney Character to the other Guests at any time.
Disney Cast Members have the right to ask you to modify or change or remove your costume, or even deny entrance, if they do not deem it's appropriate.
Regarding the Walt Disney World Moms Panel, I have to tell you it has been one of the most wonderful experiences of my life! To be selected, you must apply online during the annual search process. Check the
Disney Parks Blog on a regular basis to stay informed as to when the next search begins! Sending you lots of Pixie Dust in your pursuit of this magical dream!